Cardiac pacing leads are well known and widely employed for carrying pulse stimulation signals to the heart from a battery operated pacemaker, or other pulse generating means, as well as for monitoring electrical activity of the heart from a location outside of the body. Electrical energy is applied to the heart via an electrode to return the heart to normal rhythm. Some factors that affect electrode performance include polarization at the electrode/tissue interface, electrode capacitance, sensing impedance, and voltage threshold. In all of these applications, it is highly desirable to optimize electrical performance characteristics at the electrode/tissue interface.
Electrode materials intended for low threshold cardiac pacing or neuro-stimulation are required to have high electrical efficiency and minimal polarization loss during charge injection. The electrode used for electrical stimulation also needs to have high impedance, meaning a small geometrical surface area, in order to prevent premature battery depletion. The small geometric area translates into high current density that can cause the electrode potential to exceed the limits of a safe electrochemical window where no gas evolution or corrosion of the electrode takes place.
Charge injection efficiency is directly related to electrochemically active area and capacitance of the implantable electrode. Electrode capacitance is directly proportional to charge storage capacity (mC/cm2). The presence of a pseudo-capacitive material increases the electrode charged-storage capacity and allows for safe deliveries of charge densities.